Most semiconductor and related products, for example transistors, diodes, light emitting diodes, MEMS devices, planar waveguide structures and integrated circuits, are fabricated in the form of a large number of elements manufactured simultaneously on a large wafer. This wafer is typically composed of Si, GaAs, GaP, InP, Sapphire, or other material. The creation of devices is most often performed using conventional fabrication techniques such as photolithography, oxidation, implantation, deposition, etching, epitaxial growth, and/or spin coating. Upon completion of these device wafers, the individual devices must be singulated, a process which is typically referred to as “dicing.” The individual devices are referred to as “die” or “dice.” The area on the wafer in between active parts of adjacent die is referred to as the “street” or “dice lane.” The streets are limited to a minimum width because of the wafer material which is removed or destroyed during the dicing process. The wafer area which is completely removed by the dicing process is called the “kerf,” while the rest of the street must accommodate any damage zone around the cut and any misalignment or deviation from straightness of the cut.
Conventionally, dicing is performed by the use of a wafer saw or by the technique of “scribe and break,” where the wafer is notched, often by a diamond point, and is then cleaved along this scribe line. Due to issues with scribe and break such as low yield, dicing saws have taken over in recent years as the predominant technique for dicing wafers. Conventional slicing blades typically have a narrow dimension of about 50 to 200 μm along their cutting axes and produce cuts that are wider than the blades. The slicing blades currently need to be this wide to withstand stresses of making straight cuts through the strength and thickness of conventional wafers, for example. The wide cuts made by the mechanical cutting blades often significantly reduce the number of rows and columns of die that can be fit onto each wafer.
Skilled persons will also note that dicing blades tend to wear relatively quickly such that the widths of their cuts may vary over time. In some cases, the blades can be inadvertently bent and then such blades produce curved or slanted cuts or increased chipping. The dicing process creates small chips as it creates sharp edges and sharp corners along singulation paths.
FIG. 1 is a simplified representation of a traditional continuous cutting profile 8. Traditional laser cutting employs sequentially overlapping spots from consecutive laser pulses to continuously scan through an entire cut path. Numerous complete passes are performed until the target is severed along the entire cut path. When the target material is thick, many passes (in some cases over 100 passes) may be necessary to complete the cutting process, particularly with limited laser power.
A method for dicing wafers and increasing laser cutting throughput for thick materials is, therefore, desirable.